Diabetes care involves periodically checking the blood glucose level of a bodily fluid such as blood. Based on the measured bodily fluid level, a diabetic may take one or more steps such as injecting insulin or consuming carbohydrates to bring the level back to a desired level.
Glucose Meters
FIG. 1 illustrates a conventional blood glucose meter 100 (see U.S. Design Pat. No. D393,313, which is hereby incorporated by reference). The meter 100 includes a test strip slot 102, a display 104 and one or more operational buttons 106. Although not shown in FIG. 1, the meter 100 also includes component circuitry for receiving signals that depend on the glucose level of a fluid applied to a strip that is inserted into the slot 102, and component circuitry for determining the glucose level based on the received signals. FIG. 2 illustrates a blood glucose meter 200 with display 104 and operational buttons 106, and also having a glucose test strip 202 inserted into a slot 102 for testing a body fluid sample applied to the strip 202.
Glucose Sensors
Small volume (e.g., less than 0.5 microliter), in vitro, electrochemical sensors are used with Freestyle® and Freestyle Flash™ glucose meters (see http://abbottdiabetescare.com, which is hereby incorporated by reference). These test strip sensors generally include a working electrode on a first substrate, a counter (or counter/reference) electrode on a second substrate, and a sample chamber. The sample chamber is configured so that when a sample (e.g., of blood) is provided in the chamber, the sample is in electrolytic contact with both the working electrode, the counter electrode and any reference electrodes or indicator electrodes that may be present. This allows electrical current to flow between the electrodes to affect the electrolysis (electrooxidation or electroreduction) of the analyte. A spacer is generally positioned between first substrate and second substrate to provide a spacing between electrodes and to provide the sample chamber in which the sample to be evaluated is housed.
FIGS. 3A-3C illustrate one of these test strips (see U.S. Pat. No. 6,942,518, which is assigned to the same assignee as the present application, and is hereby incorporated by reference). This configuration is used for side-filling, and end-filling is an alternative. FIG. 3A illustrates a first substrate 340 with a working electrode 342. FIG. 3B illustrates a spacer 344 defining a channel 346. FIG. 3C (inverted with respect to FIGS. 3A and 3B) illustrates a second substrate 348 with three counter (or counter/reference) electrodes 350, 352, 354. This multiple counter electrode arrangement can provide a fill indicator function, as described below. The length of the channel 346 is typically defined by the two parallel cuts along the sides 356, 358 of the sensors.
Glucose test strip sensors can be manufactured adjacent to one another, as illustrated in FIGS. 4A-4B. Such positioning during manufacture produces less waste material. This often results in better efficiency as compared to other techniques, such as individually placing components within the individual channels of test strip sensors.
General Method for Manufacturing Glucose Sensors
FIGS. 4A-4B illustrate the processing of a sheet of test strips. Referring now to FIGS. 4A and 4B, one example of a method for making thin film sensors is generally described, and can be used to make a variety of sensor arrangements. When the three layers of the test strips of FIGS. 3A-3C, e.g., are assembled, a sensor is formed.
In FIGS. 4A and 4B, a substrate 400, such as a plastic substrate, is moving in the direction indicated by the arrows. The substrate 400 can be an individual sheet or a continuous roll on a web. Multiple sensors can be formed on a substrate 400 as sections 422 that have working electrodes thereon and sections 424 that have counter electrodes and indicator electrodes thereon. These working, counter and indicator electrodes are electrically connected to corresponding traces and contact pads. Typically, working electrode sections 422 are produced on one half of substrate 400 and counter electrode sections 424 are produced on the other half of substrate 400. In some embodiments, the substrate 400 can be scored and folded to bring the sections 422, 424 together to form the sensor. In some embodiments, as illustrated in FIG. 4A, the individual working electrode sections 422 can be formed next to or adjacent each other on the substrate 400, to reduce waste material. Similarly, individual counter electrode sections 424 can be formed next to or adjacent each other. In other embodiments, the individual working electrode sections 422 (and, similarly, the counter electrode sections 424) can be spaced apart, as illustrated in FIG. 4B.
Radio Frequency Identification (RFID)
RFID provides an advantageous technology for remotely storing and retrieving data using devices called RFID tags. An RFID tag is a small object, such as an adhesive sticker, that can be attached to or incorporated into a product. There are passive and active RFID tags. Passive RFID tags are small devices that are generally used at shorter range and for simpler tracking and monitoring applications than active tags. Passive tags generally act over ranges up to 3-5 meters, and a few hundred are typically readable simultaneously within three meters of a reader. Because they are powered by radio waves from RFID tag reader, passive tags do not use a battery. Therefore these devices are generally inexpensive and smaller than active tags, and can last long. Active RFID tags have a power source, such as a battery, and generally have longer range and larger memories than passive tags. For example, active tags generally act over ranges up to 100 meters, and thousands of tags are typically readable simultaneously within 100 meters of a reader. For more details on passive and active RFID tags, see http://RFID-Handbook.com, which is hereby incorporated by reference.
RFID System
An RFID system generally includes an RFID tag and RFID reader. An RFID tag includes an antenna and digital memory chip. An RFID reader, also called an interrogator, includes an antenna and a transceiver, and emits and receives RF signals. RFID readers can read tags and can typically write data into the tags. For example, FIG. 5 schematically illustrates component circuitry of a passive RFID tag. A transceiver/receiver 502 of an RFID reader 505 is directionally coupled 504 to an antenna 506 of the reader 505. An RFID transponder 510 includes an antenna 512 (e.g., a dipole antenna) and memory 514.
It is desired to incorporate RFID tag technology into glucose test strips, test strip vials and/or boxes of strips. It is also desired to incorporate RFID reader into glucose meters.